Many industrial processes require non-invasive, non-destructive measurement of temperature within a mass of material, for example, processed food product inspection and also medical applications.
Travelling wave and induction field surface-contact type antennas have previously been used for medical applications. However, these types of antennas are not well suited to many envisaged applications. In particular, the following problems are evident:
(1) The weighting functions for this class of antenna are strongly biased to a region in direct contact with the antenna, i.e., the induction or near-field zone. The radiometric temperature measurement is, therefore, strongly biased to an object's surface region adjacent to the antenna.
(2) If there is a region of low dielectric loss material between the antenna and the glossy material of an object, such as a packaging air gap, wave modes propagating perpendicular to the antenna measurement axis may be set up, dramatically reducing the radiometric coupling to the product.
(3) If an object is electromagnetically thin in the direction of the antenna measurement axis, radiation from sources beyond the object will be coupled into the antenna together with the object material radiation giving a false temperature measurement (e.g., fluorescent lighting microwave radiation).
(4) If there is a region of low dielectric loss material between the antenna and the lossy material of an object (as in (b) above), radiation from sources around the antenna and the object will enter the antenna, again leading to a false temperature measurement.
Thermal/Infra-red imaging also only gives a surface reading and has problems in penetrating water and grease. It is also not possible to see through packaging for food.
It is an object of at least one embodiment of at least one aspect of the present invention to obviate/mitigate one or more of the disadvantages of the prior art.
It is also an object of at least one embodiment of at least one aspect of the present invention to provide a method of using natural microwave thermal radiation to measure the temperature of an object.